Even though the automotive industry has over the years, if for no other reason than seeking competitive advantages, continually exerted substantial efforts to increase the fuel economy, of automotive engines, the gains continually realized thereby have been deemed by various governmental bodies as being insufficient. Further, governmental bodies have also imposed regulations specifying the maximum, and very stringent, permissable amounts of carbon monoxide (CO), hydrocarbons (HC) and oxides of nitrogen (NO.sub.x) which may be emitted by the engine exhaust gases into the atmosphere.
Unfortunately, the available technology employable in attempting to attain increases in engine fuel economy is, generally, contrary to that technology employable in attempting to meet the governmentally imposed standards on exhaust emissions.
For example, the prior art, in attempting to meet the standards for NO.sub.x emissions, has employed a system of exhaust gas recirculation whereby at least a portion of the exhaust gas is re-introduced into the cylinder combustion chamber to thereby lower the combustion temperature therein and consequently reduce the formation of NO.sub.x.
The prior art has also proposed the use of engine crankcase recirculation means whereby the vapors which might otherwise become vented to the atmosphere are introduced into the engine combustion chambers for burning.
The prior art has also proposed the use of fuel metering means which are effective for metering a relatively overly-rich (in terms of fuel) fuel-air mixture to the engine combustion chamber means as to thereby reduce the creation of NO.sub.x within the combustion chamber. The use of such overly-rich fuel-air mixtures results in a substantial increase in CO and HC in the engine exhaust, which, in turn, requires the supplying of additional oxygen, as by an associated air pump, to such engine exhaust in order to complete the oxidation of the CO and HC prior to its delivery into the atmosphere.
The prior art has also proposed the use of (generally relatively costly) fuel metering injection means instead of the predominantly employed carbureting means and, under superatmospheric pressure, injecting the fuel into either the primary induction passage means, the engine intake manifold or directly into the cylinders of a piston or rotor type internal combustion engine.
It is anticipated that the said governmental bodies will be establishing even more stringent exhaust emission levels of, for example, 1.0 grams/mile of NO.sub.x (or even less).
The prior art, in view of such anticipated requirements with respect to NO.sub.x, has suggested the employment of a "three-way" catalyst, in a single bed, within the stream of exhaust gases as a means of attaining such anticipated exhaust emission limits. Generally, a "three-way" catalyst (as opposed to the "two way" catalyst system well known in the art) is a single catalyst, or catalyst mixture, which catalyzes the oxidation of hydrocarbons and carbon monoxide and also the reduction of oxides of nitrogen. However, it has been discovered that a difficulty with such a "three-way" catalyst system is that if the fuel metering is too rich (in terms of fuel), the NO.sub.x will be reduced effectively, however, the oxidation of CO will be incomplete. On the other hand, if the fuel metering is to lean, the CO will be effectively oxidized but the reduction of NO.sub.x will be incomplete.
It should be apparent that in each of the hereinbefore disclosed prior art proposals (only selected ones being set forth) the accurate metering of the fuel becomes extremely important to the overall attainable success of that particular proposal.
In carburetors, it is accepted practice to employ what is usually referred to as a primary or main venturi within the induction passage means. The motive fluid or air passing through such induction passage means must pass through the throat of such venturi and, in so doing, creates a reduction in the static pressure in the motive fluid in the vicinity of the throat. Generally, the static pressure varies as the square of the velocity of the motive fluid or air flow through the venturi throat. Knowing the physical size (flow area) of the venturi throat and the velocity of flow therethrough, it becomes possible to compute (for any set of given conditions) the volume rate as well as the mass rate of air flow. It then becomes a calculable solution as to what size metering restrictions etc. should be employed as to result in the delivery (by aspiration) of fuel to the induction passage (for each of such set of given conditions) while employing the generated venturi static pressure as one of the pressures in determining the fuel metering pressure.
In many forms of fuel injection systems, a motive fluid or air induction passage having a venturi therein is also employed. Often, in such arrangements, the primary purpose of such a venturi is to create a pressure signal or pressure signals (indicative of rate of flow of air through the induction passage) which are, in turn, employed by and responded to by related control means within the fuel injection system as to accordingly or in response thereto alter or control the fuel volume and/or mass rate of metered fuel flow.
It is obvious that the only way the consuming public can afford to purchase any such fuel metering system is for the manufacturer or manufacturers thereof to employ techniques of mass-production. One of such techniques adopted by (for all practical purposes) every manufacturer of carburetors and/or fuel injection systems employing a venturi induction passage is to die cast such structure which defines the induction passage and venturi. Die casting has been accepted and acknowledged as a very accurate method of repetitive manufacture of a large quantity of identical parts. In such casting, the die assemblies are usually made as to include a plurality of mold cavities thereby producing a like plurality of castings (die cast parts) for each cycle of machine operation. This is also an accepted technique to minimize the cost per-part-cast in terms of machine amortization as well as labor costs.
In situations where a plurality of mold cavities are formed, such are almost invariably formed (machined) from a single "master" so that the mold cavities are, for all practical purposes, identical to each other. Generally, the same applies to where two or more vendors supply the same die cast parts to a single vendee who will employ such cast parts in related structures or systems.
Generally, in die casting such venturi bearing induction passage structures, the die cavity defines the external configuration of the structure while suitable cores are employed for defining internal configurations. Since the induction passage and venturi are internal configurations, core means are employed for the definition thereof. Further, since the venturi throat is the smallest transverse or cross-sectional area in the cast induction passage, at least two cores are needed to enable core withdrawal after casting.
Accordingly, in the die casting of such induction passage structures with a venturi, first core means is employed to define, generally, the configuration of the induction passage and venturi upstream of the venturi throat while second core means is employed to define, generally, the configuration of the induction passage and venturi downstream of the venturi throat. As should be apparent, such first and second core means, at the respective jutting ends, are juxtaposed to each other during the actual casting operation. However, because of manufacturing techniques, directions of movement of the respective die blocks and cores (as during closing and opening movements) it becomes practically impossible to bring the juxtaposed ends of the induction passage and venturi cores against each other to form a fluid-tight passage therebetween. As a consequence thereof, a generally transversely extending portion of die cast metal results at the throat of the venturi, such commonly being referred to as flashing. Experience has shown that such flashing may be, for example, of a thickness in the order of 0.20 inch.
Heretofore, it has been accepted practice to take such cast induction passage and venturi structures and then accurately machine-out (cut out) the flashing to define the desired venturi throat area.
However, it has been unexpectedly discovered that even though every precautionary step has been believed to have been taken in order to assure uniformity of such resulting cast and venturi machined induction passage and venturi structures, when such structures are employed in an overall metering environment or system, substantial and totally unexpected variations in the ultimate fuel metering characteristics are experienced.
That is (for example, with any one particular design of an induction passage and venturi structure) even though the die cavities and cores are made from the same master, and even if the flashing is cut out of all of the cast structures with the same tool, there are unexpected variations experienced in ultimate metering as between any two systems employing respective ones of such induction passage and mechined venturi throat structures. Further, such variations are also found where two or more of such induction passage structures are sequentially cast in the same die cavity and machined by the same tool for removing the flashing.
Because of such variations, the attainable accuracy of the associated total fuel metering system is limited and often becomes significantly less than that otherwise anticipated.
It has now been discovered that not only must the flashing be accurately removed from the throat of the cast venturi, but that the surface portion of the venturi, upstream of the throat, must also be re-formed, as by coining or the like, as to assure proper entry of the air (motive fluid) into and through the venturi throat. Even though the precise reasons are not known, it nevertheless appears that there are extremely slight variations, as between any two structures, in the upstream portion of the venturi. If this belief that such slight variations do exist is, in fact, correct, then it would appear that such variations might occur as a result of slight variations: (a) in the temperature of the mold or die assembly during casting, (b) in the temperature of the molten metal being cast in the die assembly, (c) in variations in the thickness of various portions of the structure defining the induction passage means and the consequent variations in time-rate of heat transference, or (d) any combination of the preceding or any other unknown factors.
Accordingly, the invention as herein disclosed and claimed is primarily directed to the solution of the aforestated as well as other related and attendant problems.